This invention relates to a grinding machine motor with a torque sensor that covers the normal torque range of grinding machines while also serving the function of gap elimination.
In order to carry out the grinding operation with high precision and high efficiency, it is essential that the process be carefully monitored and controlled. In the monitor and control of the grinding process, what is required is a sensor capable both of measuring the grinding torque (the most important factor concerned) and of providing adequate response, good reliability and high resolution at the time of low torque (gap elimination capability). Up to now, there has been no sensor available capable of properly carrying out both of these functions.
More specifically, the torque meters which have been used widely in connection with grinding machines cannot be easily adapted for use in gap elimination. On the other hand, the method of torque detection by a wattmeter connected to the motor circuit does not provide adequate response or sufficient resolution. These same problems are also found in another method which uses strain gauges attached to the work center. What is more, none of these conventional methods has made it possible to detect any change in torque before the grinding wheel comes into contact with the workpiece.
In fact, however, as the grinding wheel comes close to the workpiece, there is a slight increase in the motor torque due to the coolant. If a torque sensor capable of covering the torque range encountered in ordinary grinding and having a sufficiently high degree of resolution in the low torque region can be provided, such a sensor would be able to detect the rise in motor torque just before the grinding wheel touches the workpiece and, because of this, would be able to provide effective gap elimination capability. Moreover, use of a torque sensor capable of providing the function of gap elimination in this way would also make it possible to advance the grinding wheel toward the workpiece at high speed up to a point immediately preceding the workpiece without any fear of the grinding wheel colliding with the workpiece. This would be highly effective for reducing the grinding cycle time and would not require any major modification to be made to the signal processing system of the conventional grinding machine.